A pilot study comparingin vitroefficacy of topical preparations against veterinary pathogens

Background Topical antimicrobial agents are important for the management of cutaneous infections. For topical antimicrobial agents, in vitro efficacy data are limited. Objectives To determine and compare the minimum bactericidal/fungicidal concentrations ( MBC s/ MFC s) of several topical antimicrobial agents against veterinary pathogens. Materials and methods Two chlorhexidine, two oxychlorine based products (NaOCl & HOCl) lime sulfur ( LS ), manuka honey ( MH ) and hydrocortisone aceponate ( HCA ) were tested against American Type Culture Collection ( ATCC ) and clinical isolates: meticillin susceptible and resistant Staphylococcus pseudintermedius ( MSSP ), qac A/B carrying MSSP , antimicrobial susceptible and extended spectrum beta‐lactamase producing Escherichia coli , multidrug‐resistant Pseudomonas aeruginosa and Malassezia pachydermatis . The MBC s/ MFC s were measured, where available, using a broth microdilution method; isolates were incubated for 3 and 10 min. Results Chlorhexidine and isopropyl alcohol (Chl 1 ) showed significantly lower MBC s (0.46 mg/L –937.50 mg/L, P = 0.027) compared to chlorhexidine and climbazole (Chl², 58.59 mg/L–1875 mg/L). Na OC l and HOC l showed excellent antimicrobial activity with HOC l having significantly lower MBC s compared to Na OC l (0.03 mg/L–1.72 mg/L and 0.03 mg/L–1.95 mg/L, respectively, P = 0.042). The detectable MBC s for LS and HCA were high, being close to the starting concentration (5,000 mg/L and 146 mg/L, respectively). The MBC / MFC for MH was not detectable. Amongst all test products there was no significant effect of contact time or isolate resistance status. Conclusions and clinical importance Chlorhexidine, Na OC l and HOC l demonstrated low MBC s against tested organisms, suggesting potential in vivo efficacy. The selection of an appropriate antimicrobial agent, however, cannot be based exclusively upon MBC / MFC data; other factors should be considered.